Hello, Seems a bit similar to an earlier post, but this is using msvc6. The ambiguity is with "stlport\stl\_complex.h" (version 4.5.3). The error is: d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2782: ' __cdecl _STL::abs()' : template parameter 'T' is ambiguous could be 'long double' or 'const struct _STL::complex<long double> &' d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2785: ' __cdecl _STL::abs()' and 'long double __cdecl _STL::abs(const struct _STL::complex<long double> &)' have different return types d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(30) : see declaration of 'abs' d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2782: ' __cdecl _STL::abs()' : template parameter 'T' is ambiguous could be 'double' or 'const struct _STL::complex<double> &' d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2785: ' __cdecl _STL::abs()' and 'double __cdecl _STL::abs(const struct _STL::complex<double> &)' have different return types d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(30) : see declaration of 'abs' d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2782: ' __cdecl _STL::abs()' : template parameter 'T' is ambiguous could be 'float' or 'const struct _STL::complex<float> &' d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(33) : error C2785: ' __cdecl _STL::abs()' and 'float __cdecl _STL::abs(const struct _STL::complex<float> &)' have different return types d:\c_plus_plus\boost_1_29_0\boost\date_time\compiler_config.hpp(30) : see declaration of 'abs'